Delayed-type drug hypersensitivity reactions in a tertiary adult allergy clinic: A 5-year cohort study

Delayed-type drug hypersensitivity reactions (DHRs) range from maculopapular eruptions to severe cutaneous adverse reactions (SCARs). Provocation tests are unsafe in SCARs, so diagnosis depends on history, making regional data important for identifying high-risk drugs. This study aimed to retrospectively assess the clinical features and test results of patients with delayed-type DHRs in our clinic.

Adults ≥18 years with DHRs, evaluated at our clinic between 2019 and 2025, were included in this retrospective observational study. Patients with Types I-III reactions or incomplete records were excluded. Eligible cases were identified through retrospective review of medical records. Clinical data, laboratory findings, and patch and/or drug provocation test results were obtained from medical files.

Thirty-three patients were included, of which 57.6% were females, and the median age was 40 years (19-70). The most common phenotype was maculopapular exanthem (n = 15, 45.5%), followed by fixed drug eruption (FDE) (n = 8, 24.2%). Seven patients (21.2%) had SCAR, including toxic epidermal necrolysis (TEN, n = 3), Stevens-Johnson syndrome (SJS, n = 1), SJS/TEN overlap (n = 1), drug-related eosinophilia and systemic symptoms (n = 1), and generalized bullous FDE (n = 1). Six patients (18.2%) required hospitalization, four of whom were managed in an intensive care or burn unit. Seventeen patients (51.5%) had a single likely culprit drug, while the remaining patients were taking multiple medications. Antimicrobials (41.3%), particularly beta-lactam antibiotics, and nonsteroidal anti-inflammatory drugs (NSAIDs, 29.3%), were the most frequently implicated drug groups. Nine patients underwent diagnostic testing (patch testing n = 6, delayed intradermal testing n = 3), with four positive results.

Antibiotics, especially beta-lactam antibiotics and NSAIDs, were the leading culprit drugs. Polypharmacy complicates culprit identification, particularly in SCAR cases, underscoring the need for cautious prescribing and avoidance of unnecessary medications.